I think something is wrong with the question you have given
it should be
6x10x8 and NOT 6x1x8(can you cut a cube of 2cm side from a prism of any of its dimension 1cm)
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As ADARSH said, you can't just 'cut' a rectangle with one side of length 1 into cubes have all sides of length 2. The only way this problem makes sense is if we are allowed to "glue" pieces together. In that case, the number of cubes is just the volume of the prism divided by the volume of one cube.